The importance of development of drug-delivery systems are increasing rapidly throughout the world. The reason is simple: the necessity to cut public health expanses demand lower costs and higher efficacy. To meet this demand, many efficient drugs currently in use will be reformulated within delivery systems that can be value-added for optimal molecular activity. The invention is a novel method of core-shell nanoparticle preparation of protein drugs or protein-bound active compounds, which provides a relatively easy and inexpensive way to formulate sustained release products. The solid core of the nanoparticles is prepared by precipitation with salts, and they are subsequently coated with polyelectrolyte multilayers using the electrostatic self-assembly (ESA) method, or in other words, layer-by-layer self-assembly. Pharmacokinetic studies in rabbit models detected steady INF release for 10 days after subcutaneous injection administration of the nanointerferon formulation.